Rheopectic lithium soap grease and method of preparation therefor



3,679,341 RHEOPECTIC LETHEUM SOAP GREASE AND METHGD F PREPARATEGN THEREFGR William R. Coons, in, Port Arthur, William R. Honcho,

Groves, and Gordon S. Bright, Port Arthur, Ten, as-

signers to Texaco ine, a corporation of Delaware No Drawing. Fiied Bee. 22, 1958, Ser. No. 781,900

13 Claims. ((31. 252-41) This invention relates to lithium hydroxy fatty acid soap greases of the so-called rheopectic type and to an improved method of making them.

The greases to which this invention relate are fluid greases of low soap content which thicken readily to a grease consistency upon working under conditions involving moderate shearing to which the grease is subjected in automotive bearings. These greases can be shipped in tank cars and otherwise handled as liquids, and they therefore ofier an important advantage in their case of transportation and handling over the conventional lubricating greases. Greases obtained in accordance with this invention are adapted particularly for use in centralized automotive lubricating systems wherein the lubricant is fed to the bearings from a central reservoir through small diameter tubes.

Lithium hydroxy fatty acid soap greases are ordinarily prepared by methods which involve heating a mixture of lithium soap and lubricating oil to a temperature above the melting point of the soap, cooling the mixture rapidly, and then milling with high shearing rates in order to convert the gel-like product into a grease of the proper texture and consistency. A convenient low temperature method is also described by O, P. Puryear and H. V. Ashburn in US. 2,450,25. 5 and US. 2,45 0,219-20, which comprises forming a lithium hydroxy fatty acid soap in the presence of a small amount of lubricating oil at a temperature below the melting point of the soap and cooling the hot grease mixture by adding the remainder of the lubricating oil employed in the grease at a lower temperature. This method produces lithium hydroxy fatty acid soap greases in very poor yields, and these greases ordinarily undergo only small changes in consistency upon shearing. These conventional methods for preparing lithium hydroxy fatty acid soap greases are therefore not suitable for preparing greases of the type with which the present invention is concerned, since fluid greases prepared by these methods require severe shearing in order to produce a good grease texture and consistency.

The method of the present invention comprises essentially forming a lithium hydroxy fatty acid soap in the presence of a relatively large amount of lubricating oil, heating the grease mixture to a maximum temperature during the grease making process above about 300 F. but substantially below the melting point of the soap, and cooling the grease mixture slowly without any substantial quenching effect being obtained by oil addition. The saponification mixture employed comprises lubricating oil and saponifiable material in a ratio of at least about 3:1, and preferably at least about 6:1 by weight. Most advantageously, the ratio of lubricating'oil to saponifiable material employed is from about 12:1 to about 25:1 by weight, or even higher. Additional lubricating oil is added to the grease mixture during the heating if necessary so that the grease mixture before cooling contains at least the major part of the lubricating oil employed in the finished grease.

We have found that by employing suitably low amounts of soap, fluid greases are obtained by this method which develop a grease consistency very rapidly when they are subjected to a moderate shearing action, of the order to which the grease is subjected in automotive hearings in ited States Patent 0 3,?9,34-l Patented Feb. 26, 1%63 "ice service. Photomicrographs of these greases show that this result is due chiefly to the amount and character of soap fiber agglomeration which takes place under the described conditions. The desired initial fluidity of the product is due to the large amount of agglomerate formation, which is unexpectedly equal to or even higher than that obtained by the low temperature method of Puryear and Ashburn, wherein the soap is formed in a relatively concentrated lubricating oil solution. However, the charactor of the agglomerates formed by the two methods is very different, since those obtained by the method of this invention are readily separated into the individual soap fibers by even moderate shearing, while the products ob tained by the Puryear and Ashburn method require very severe shearing in order to disperse the strongly agglomerated soap fibers sufficiently to produce any substantial increase in consistency of the product.

The fluid greases obtained as described above ordinarily have a slightly grainy texture, due to the large amount of agglomeration of the soap fibers which occurs. This graininess is not ordinarily objectionable, since the grains are soft and easily dispersed, and a smooth grease of buttery texture is formed readily when the grease is employed in automotive bearings. However, we have found that smooth products, especially suitable for use in centralized automotive systems, may be obtained by carrying out the preparation with circulation of the grease mixture through an external recycle line during at least a portion of the heating cycle, preferably during the dehy-' dration step, and very advantageously during at least a portion of the cooling cycle also.

tion should be at a rate below about 10,000 reciprocal seconds and preferably at a rate below about 5000 reciprocal seconds. Pumps which give suitably low shearing rates and which are otherwise efiective for the purpose include particularly positive displacement pumps, including both rotary and reciprocating pumps, although centrifugal pumps may also be employed under suitable conditions.

The greases of this invention comprise a lubricating oil as the chief component and about 26 percent by weight of a lithium soap of a hydroxy fatty acid material comprising at least about 35 percent by Weight of a hydroxy fatty acid material. Preferably the soap comprises at least a major amount, and most suitably at least about percent by Weight of a lithium hydroxy fatty acid soap. These greases are initially in the form of fluids, having ASTM. unworked penetrations at 77 F. above 400, and ordinarily having ASTM penetrations (calculated) in about the range 420520. After shearing at rates above about 100,000 reciprocal seconds, they become N.L.G.I. No. 0-2 grade greases. The preferred greases of this invention contain about 3-5 percent by weight of the lithium soap and form greases of N.L.G.I. No. 1 grade upon shearing.

' Suitable soap forming hydroxy fatty acid materials which may be employed in the production of these greases are essentially saturated hydroxy fatty acids containing 12 or more carbon atoms and one or more hydroxyl groups separated from the carboxyl group by at least one carbon atom, and the glycerides and lower alkyl esters of such acids. Preferably, the acid contains about 16 to about 22 carbon atoms per molecule. Such materials may be obtained from naturally occurring glycerides or produced synthetically by methods such as the hydroxylation of fatty acids or the hydrogenation of ricinoleic acid or castor oil. Particularly suitable materials of this character are 12-hydroXy-stearic acid, the methyl ester thereof, and hydrogenated castor oil. Such hydroxy fatty acid materials may be employed in the saponification in admixture with saponifiable materials of the conventional types, as disclosed, for example, by H. V. Ashburn and O. P. Puryear in US. 2,450,220. The preferred saponifiable materials of this type are saturated fatty acids containing from about 16 to 24 carbon atoms per molecule and the glyoerides of such acids.

The lubricating oils employed in these greases include particularly the conventional mineral lubricating oils, having Say'bolt Universal viscosities in the range from about 70 seconds at 100 'F. to about 225 seconds at 210 F., and synthetic hydrocarbon oils having viscosities in this range, such as those obtained by cracking and polymerizing products of the Fischer Tropsch process and the like. The mineral lubricating oils may be either napthenic or paraflinic oils, or blends of different oils of these types. Other synthetic oleaginous compounds such as polyesters, polyethers, etc. having viscosities within the lubricating oil viscosity range may also be employed in these greases as at least part of the lubricating oil component. Suitable compounds of this type include particularly the aliphatic discarboxylic acid diesters, such as, for example, (ii-2- ethylhexyl seb'acate, di(secondary amyl) sebacate, di-2- ethylhexyl azelate, di-isooctyl adipate, etc. However, a lubricating oil which is substantially unreactive under the saponifi'cation conditions is preferably employed in the saponi-fication mixture. Mineral lubricating oils are particularly suitable for this purpose.

Various additives of the usual types such as corrosion inhibitors, oxidation inhibitors, extreme pressure agents, antiwear agents, etc., may be employed in these greases. Suitable oxidation inhibitors include particularly those of the amine type, such as diphenylamine, phenylalphanaphthylamine, tenamethyl diaminodiph-enyl methane,

etc. Very advantageously, the greases may contain frornabout 3 to 12 percent by weight of a sulfurized fatty oil such as sulfurized sperm oil, containing about 5-15 percent by weight of sulfur, and about 1 to 3 percent by weight of a lead soap such as lead naphthenate. Lead naphthen-ates obtained from relatively low molecular weight naphthen-ic acids, such as those. having molecular weights in about the range from about 120 to about 235, and preferably in the range from about 200 to about 230, are particularly suitable for this purpose. By means of this additive combination, good extreme pressure properties are imparted to these lithium hydroxy fatty acid soap greases without any substantial impairment of their rheopectic properties.

In carrying out the grease preparation, the grease kettle is charged with the saponifiable hydroxy fatty acid material and lubricating oil in suitable proportions as discussed above, water, and lithium hydroxide or other suitable basic lithium compounds in approximately the stoichiometric amount required to react with the saponiliable material. The amount of water employed is preferably sutficient to give about a5 to 20 percent lithium hydroxide solution. These materials may be introduced into the grease kettle in any order desired. The kettle is heated at a rate such that the charge is gradually brought up to about 300 F. in a length of time sufficient to accomplish the saponification and substantially complete dehydration, as shown by the cessation of foaming. Ordinarily this will require 'at least about 4 hours, although either slower or faster heating may be employed if desired. The grease mixture is then heated to a maximum temperature in the range from about 300 F. to a temperature at least about F. below the melting point of the soap. The grease mixturei-s maintained at a tem- I erature above about 300 F. for a suificient time to complete the dehydration, which may require from a few minutes up to an hour or longer. The grease mixture is finally cooled slowly with continued stirring, suitably at a rate below about 10 F. per minute, and preferably at a rate below about 5 F. per minute. The cooling is carried out by any convenient means, such as by passing cooling fluid through the kettle jacket. Any additives employed may be mixed in during or after the cooling when the grease mixture is at a suitably low temperature. The grease is finally drawn at a temperature below about 200 F.

Additional lubricating oil may be added at any time during the heating cycle, preferably while the grease mixture is being heated at a temperature above about 300 F. and with the avoidance of any substantial quenching.- Where the saponification mixture contains lubricating oi and soap in a ratio below about 10: 1, additional lubricating oil is preferably added before the mixture is cooled below about 300 P. so as to give an oil-soap ratio of at least about 10:1, and preferably containing at least about percent by weight of the total oil contained in the finished grease. Preferably, not more than a minor portion of the total oil, such as below about 25 percent by weight, is added during or after the cooling. The oil addition is preferably carried out slowly, such as at a rate below about 0.1 pound of oil per minute per pound of grease mixture, and most suitably at a rate below about 0.05 pound of oil per minute per pound of grease mixture.

The preferred method of carrying out the grease preparation comprises continuously withdrawing a minor stream of the grease mixture and pumping it through an outside recycle line on the grease kettle during at least a part of the heating cycle. The grease is circulated suitably at a rate such that the volume of grease recirculated equals the volume of the batch in less than about 20 minutes, and preferably in about 0.5-10 minutes. With particular advantage, the circulated stream of grease mixture is returned at the top of the grease kettle, at a point above the surface of the grease mixture Within the kettle. This provides an increased opportunity for the evaporation of water and thereby greatly shortens the dehyd.ra tion time required, so that the disadvantage of a longer dehydration time otherwise required with this method because of the large amount of lubricating oil present in the saponification mixture may be substantially or entirely overcome.

As an example of a preferred embodiment of this invention, rheopectic extreme pressure greases were prepared having the following composition in percent by weight:

Lithium lZ-hydroxystearate 3-5 Glycerine 0.3-0.5 Lead naphthenate 1.0-2.0 Sulfurized sperm oil 6.0-12.0 Free alkali (LiOH) 0.05-0.20 Mineral lubricating oil of-60.80 SUS viscosity at 210 F Remainder The greases were prepared in about 65 pound batches, employing a pound capacity jacketed kettle equipped with a stirrer and an outside recycle line for circulating, grease from the bottom to the top of the kettle. The recycle line consisted of about 9.25 feet of smooth 1 /2 inch pipe containing a 1 /2 inch Roper gear pump. The method of grease preparation comprised saponifying hydrogcnated caster oil in 'situ in the presence of at least half of the mineral lubricating oil employed in the grease, resulting in an oil-fat ratio in the saponification mass of at least about 12:1. Following the saponificatiou, the saponified mass was heated to a temperature in about the range 300-325 F. and maintained at a temperature within this range while any additional lubricating oil employed in the grease was added slowly, at a rate below;

about 3 pounds per minute. The grease mixture was then allowed to cool at a rate below about 5 F. per minute. The additives were added to the grease mixture when it was at a temperature below about 200 F. Circulation of the grease mixture from the bottom to the top of the kettle was carried out during the dehydration at a rate of about 20-120 pounds per minute of grease mixture circulated. In some of the preparations the grease mixture was also circulated during the saponification and heating at above 300 F, and during a part of the cooling time, the total time during which the circulation was carried out being 'rom about 1 to about 3 hours. The amount of work expanded in circulating the grease mixture was below 50 foot pounds per second per pound of grease circulated.

These greases were also prepared satisfactorily in 200 pound batches in a Dowtherm heated kettle equipped with a recycle line containing a Yale and Towne Model 20 DV piston-type pump. The greases were circulated at a rate of gallons per minute for about 6 hours during the grease preparation, including both the heating and cooling cycles. The amount of work expended in circulating the grease mixture, based upon the power consumption, was about 5-20 foot pounds per second per pound of grease circulated.

The products obtained as described above were smooth liquids, having unworked penetrations generally in the range from about 420 to 500, calculated from determinations made by a modified ASTM cone penetration test, wherein a counterbalancing weight is applied to the penetrcmeter at the top. Upon shearing in automotive bearings, such as the Marlin Rockwell Corporation No. 4405 hearing at 1700 r.p.m., these liquid products attained a grease consistency, generally an N.L.G.1. No. 1 grade grease consistency, and upon shearing in a laboratory Premier colloid mill at 0.006 inch clearance, they attained a No. 1 grade or somewhat harder consistency. The sheared greases had excellent stability and other good lubricating properties, including good extreme pressure properties, represented by GK. loads in the Timken test in the range 40-70.

The rate of shearing to which the grease were subjected in milling in the Premier colloid mill is found from the following equation:

wherein Z is the rate of shearing in reciprocal seconds, D is the rotor diameter in inches, C is the clearance in inches between the rotor and the casing, and W is the speed of rotation in revolutions per second. The laboratory Premier colloid mill employed for milling these greases had a rotor diameter of 2 to 2 7 inches and was rotated at 7200 rpm, the clearance between the rotor and casing being 0.006 inch. The rate of shearing obtained was therefore of the order of 155,000 reciprocal seconds. This is far below the shearing rates ordinarily employed in milling greases, since the Premier colloid mill is normally operated at 0.002 inch clearance, resulting in a shearing rate 3 times that obtained with 0.006 inch clearance, and also, much higher shearing rates are obtained in the larger mills employed in plant scale operations due to their much larger rotors, up to about 21 inches in diameter. Lithium hydroxy fatty acid soap greases prepared by the so-called high temperature methods ordinarily require shearing rates of the order obtained by operating the mill at 0.002 inch clearance in order to convert their gel-like texture into a grease consistency. Greases of this type prepared by the low temperature method of Puryear and Ashburn generally undergo only small changes in consistency upon milling even at high shearing rates, and milling is therefore not ordinarily employed for finishing these greases.

Following is a detailed description of the method employed in the preparation of one of these greases: 3.23

pounds of hydrogenated castor oil, 2.32 pounds of a 10.5 percent aqueous solution of lithium hydroxide and 60.93 pounds of mineral lubricating oil were charged to the grease kettle. The mineral lubricating oil was a blend in a 45:55 ratio by weight of a refined naphthenic distillate oil having a Saybolt Universal viscosity of about seconds at 100 F. and a residual stock from a naphthene base crude having a Saybolt Universal viscosity of 205 seconds at 210 F. The hydrogenated castor oil was a commercial product, typical analyses of which include a saponification number of 176, an iodine No. of 2.4 and a titer, C., of 72.3. The kettle charge was heated to 180 F. and maintained at 180-190 F. for one hour to complete the saponification, heated further to about 294 F. in an additional two hours, and finally heated to 302 F. in 45 minutes. The heating was then discontinued and the grease mixture allowed to cool to 200 F. in about 65 minutes. A mixture consisting of 4.76 pounds of sulfurized sperm oil and .84 pound of lead naphthenate was then added slowly and the mixture drawn at about F. The lead naphthenate was the lead salt of naphthenic acids having a molecular weight of about 223. The sulfurized sperm oil was a commercial material consisting chiefly of sulfurized cetyl oleate. Typical tests upon this material include a sulfur content of 10.08 percent by weight, a sponification number of 138 and a gravity, API of 14.4. The grease mixture was stirred continuously throughout the grease making process and circulated from the bottom to the top of the kettle at a point above the level of the grease mixture at a rate of about 78 pounds per minute following the saponification and during the heating up to 302 F. The circulation was carried out intermittently during the heating, for a total period of about 2 hours. It was also carried out during the cooling and additive addition.

The product obtained as described above was a smooth fluid containing 4.5 percent by weight of lithium 12-hydroxystearate. It was thickened to an N.L.G.I. No. 1 grade grease upon shearing in automotive bearings. The following table shows the rheopectic and other lubricating properties of this grease and also those of a 3.0 percent soap grease prepared in substantially the same manner.

Composition:

Li 12 hydroxystearate 4. Glycerin 0. 4 Excess LiOH Pb naphthenate Sulfurized sperm oil Mineral lubricating oil- Appearance Penetration, modified ASIM method:

Oil separation Timken Test:

O.K. load, lbs

1 Remainder. Smooth liquid. 3 Too soft.

As shown by the table, the above greases were smooth liquids which hardened over 100 points both in unworked and worked penetrations upon shearing in a laboratory Premier colloid mill at 0.006 inch clearance and in an automotive ball and roller bearing. Very surprisingly,

7 these greases gave no leakage from the bearing in the torque breakdown test, although they were poured into the bearing in liquid form, showing that they hardened very rapidly upon shearing.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. The process of preparing a fluid lubricating composition comprising essentially a lubricating oil as the chief component containing about 26 percent by weight of a lithium soap and having the property of thickening to a grease consistency upon shearing, which comprises essentialiy providing a saponification mixture consisting essentially of a substantially saturated saponifiable material comprising at least about 35 percent by weight of a soap-forming hydroxy fatty acid material, a basic lithium' compound in an amount corresponding approximately to the stoichiometric amount required to react with the said saponiiiable material, a minor amount of water, and a lubricating oil which is substantially nonreactive under the saponification conditions in an amount equal to at least about three times theweight of the said saponifiable material, heating the said mixture gradually up to about 300 F. over a period of time sufilcient to obtain complete saponification, further heating the resulting saponified mass up to a maximum temperature in the range from about 300 F. to about 10 F. below the melting point of the said soap for a sufficient time to accomplish dehydration, adding any additional lubricating oil required to obtain a grease mixture containing at least the maior amount of the lubricating oil contained in the finished grease before the grease mixture is cooled to below about 300 F, and thereafter cooling the sad grease mixture to the drawing temperature at a rate below about 10 F. per minute.

2. The process according to claim 1 wherein the said saponifiable material is chosen from the class consisting of IZ-hydroxy stearic. acid and the esters thereof 3. The process according to claim 1 wherein the said saponifiable material ishydrogenated castor oil.

4. The process according to claim 1 wherein the said lubricating oil is a mineral lubricating oil.

5. The process according to claim 1 wherein the ratio of lubricating oil to saponifiable material employed in the saponification is at least about 6:1.

6. The process according to claim 1 wherein the ratio of lubricating oil to sap-onifiable material employed in the saponification is within the range from about 12:1 to about 25:1 by weight.

7. The process according to claim 1 wherein the grease mixture is subiected to a small amount of shearing during the heating which is below the amount required to produce a grease consistency in the product.

8. The process according to claim 1 wherein the grease mixture is circulated through an external line during at least a part or the heating cycle at a rate such that the volume of grease mixture circulated is at least equal to the volume of the batch within about 20 minutes.

9. The process according to claim 8 wherein the grease mixture is circulated during the dehydration step.

10. The process according to claim 8 wherein the circulation is carried out during the dehydration step and the circulated stream of grease mixture is returned to the kettle at a point above the surface of the grease mixture within the kettle.

11. The process according to claim 1 carried out at substantially atmospheric pressure.

12. The process according to claim 1 wherein the grease mixture before cooling comprises at least about 75 percent of lubricating oil contained in the finished grease.

-13. The process according to claim 1 wherein the grease mixture is oooled at a rate below about 5 F, per minute.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF PREPARING A FLUID LUBRICATING COMPOSITION COMPRISING ESSENTIALLY A LUBRICATING OIL AS THE CHIEF COMPONENT CONTAIINING ABOUT 2-6 PERCENT BY WEIGHT OF A LITHIUM SOAP AND HAVING THE PROPERTY OF THICKENING TO A GREASE CONSISTENCY UPON SHEARING, WHICH COMPRISES ESSENTIALLY PROVIDING A SAPONIFICATION MIXTURE CONSISTING ESSENTIALLY OF A SUBSTANTIALLY SATURATED SAPONIFIABLE MATERIAL COMPRISING AT LEAST ABOUT 35 PERCENT BY WEIGHT OF A SOAP-FORMING HYDROXY FATTY ACID MATERIAL, A BASIC LITHIUM COMPOUND IN AN AMOUNT CORRESPONDING APPROXIMATELY TO THE STOICHIOMETRIC AMOUNT REQUIRED TO REACT WITH THE SAID SAPONIFIABLE MATERIAL, A MINOR AMOUNT OF WATER, AND A LUBRICATING OIL WHICH IS SUBSTANTIALLY NONREACTIVE UNDER THE SAPONIFICATION CONDITIONS IN AN AMOUNT EQUAL TO AT LEAST ABOUT THREE TIMES THE WEIGHT OF THE SAID SAPONIFIABLE MATERIAL, HEATING THE SAID MIXTURE GRADUALLY UP TO ABOUT 300*F. OVER A PERIOD OF TIME SUFFICIENT TO OBTAIN COMPLETE SAPONIFICATION, FURTHER HEATING THE RESULTING SAPONIFIED MASS UP TO A MAXIMUM TEMPERATURE IN THE RANGE FROM ABOUT 300*F. TO ABOUT 10*F. BELOW THE MELTING POINT OF THE SAID SOAP FOR A SUFFICIENT TIME TO ACCOMPLISH DEHYDRATION, ADDING ANY ADDITIONAL LUBRICATING OIL REQUIRED TO OBTAIN A GREASE MIXTURE CONTAINING AT LEAST THE MAJOR AMOUNT OF THE LUBRICATING OIL CONTAINED IN THE FINISHED GREASE BEFORE THE GREASE MIXTURE IN COOLED TO BELOW ABOUT 300*F., AND THEREAFTER COOLING THE SAID GREASE MIXTURE TO THE DRAWING TEMPERATURE AT A RATE BELOW ABOUT 10*F. PER MINUTE. 